Vitamin D receptor as a candidate tumor-suppressor gene in severe hyperparathyroidism of uremia

Genetic and epigenetic changes in sporadic endocrine tumors: parathyroid tumors

Parathyroid neoplasia is most commonly due to benign parathyroid adenoma but rarely can be caused by malignant parathyroid carcinoma. Evidence suggests that parathyroid carcinomas rarely, if ever, evolve through an identifiable benign intermediate, with the notable exception of carcinomas associated with the familial hyperparathyroidism-jaw tumor syndrome. Several genes have been directly implicated in the pathogenesis of typical sporadic parathyroid adenoma; somatic mutations in the MEN1 tumor suppressor gene are the most frequent finding, and alterations in the cyclin D1/PRAD1 oncogene are also firmly established molecular drivers of sporadic adenomas. In addition, good evidence supports mutation in the CDKN1B/p27 cyclin-dependent kinase inhibitor (CDKI) gene, and in other CDKI genes as contributing to disease pathogenesis in this context. Somatic defects in additional genes, including β-catenin, POT1 and EZH2 may contribute to parathyroid adenoma formation but, for most, their ability to drive parathyroid tumorigenesis remains to be demonstrated experimentally. Further, genetic predisposition to sporadic presentations of parathyroid adenoma appears be conferred by rare, and probably low-penetrance, germline variants in CDKI genes and, perhaps, in other genes such as CASR and AIP. The HRPT2 tumor suppressor gene is commonly mutated in parathyroid carcinoma.

Brown tumor of the maxillary sinus in a patient with primary hyperparathyroidism: a case report

INTRODUCTION

Brown tumors are rare focal giant-cell lesions that arise as a direct result of the effect of parathyroid hormone on bone tissue in some patients with hyperparathyroidism. Brown tumors can affect the mandible, maxilla, clavicle, ribs, and pelvic bones. Therefore, diagnosis requires a systemic investigation for lesion differentiation.

CASE PRESENTATION

We present a 42-year-old Greek woman, with a rare case of brown tumor of the maxillary sinus due to primary hyperparathyroidism. Primary hyperparathyroidism is caused by a solitary adenoma in 80% of cases and by glandular hyperplasia in 20%.

CONCLUSIONS

Differential diagnosis is important for the right treatment choice. It should exclude other giant cell lesions that affect the maxillae.

Analysis of CYP27B1, encoding 25-hydroxyvitamin D-1alpha-hydroxylase, as a candidate tumor suppressor gene in primary and severe secondary/tertiary hyperparathyroidism

CYP27B1, encoding 25-hydroxyvitamin D-1alpha-hydroxylase, converts 25-hydroxyvitamin D to its active form, 1,25-dihydroxyvitamin D, and is expressed primarily in the kidney but also in nontraditional sites including the parathyroid glands. Whereas the role of locally produced 1,25-dihydroxyvitamin D is not yet clear, it is possible that it contributes importantly to vitamin D-mediated inhibition of parathyroid cell growth, so CYP27B1 can be considered a candidate parathyroid tumor suppressor gene in that its acquired inactivation in a parathyroid cell could confer a tumorigenic growth advantage. Expression of CYP27B1 has also been reported to be altered in parathyroid neoplasms. Because detection of inactivating mutations is the central criterion for validating a candidate tumor suppressor, we directly sequenced the coding region and all splice sites of CYP27B1 in 31 sporadic parathyroid adenomas and 31 parathyroid tumors from patients with refractory secondary/tertiary hyperparathyroidism. No nonsense, frameshift, or other inactivating mutations were found, and there was no sign of homozygous deletion. Our findings indicate that CYP27B1 does not commonly serve as a classical tumor suppressor gene in the development of sporadic parathyroid adenomas or of refractory secondary/tertiary hyperparathyroidism.

The effects of retinoic acid on the insulin-like growth factor axis in primary tissue culture from hyperparathyroidism

BACKGROUND

The importance of the IGF system in HPT has been previously demonstrated. Additionally, the role of vitamin A in HPT has been reported. Retinoic acid (RA), a derivative of vitamin A, is a ligand for the IGF II receptor (IGF2R). We have evaluated the interactions of RA with the IGF system in a primary parathyroid cell culture model.

MATERIALS AND METHODS

Primary cell cultures were prepared from nine patients. Following adhesion, the cells were transferred to serum-free medium and dosed once with growth factors +/- RA for 96 hours. Proliferation was assessed by measuring tritiated thymidine incorporation.

RESULTS

Compared with the control group (100%), both IGF I and II increased DNA synthesis significantly. Retinoic acid significantly reduced the basal DNA synthesis to 82.2% +/- 4.2% compared with control (P < 0.05). Retinoic acid x10(-5) M completely abrogated the proliferative actions of IGF II (70.2% +/- 9.7%, P < 0.05) but had no significant effect on the IGF I response (P > 0.05). To evaluate the role of IGF2R or IGFBPs in mediating the actions of RA, the IGF II analogs [Leu27]IGF II (10-20-fold reduced IGF I receptor affinity) and des(1-6) IGF II (lower IGFBP binding affinity) were used. The IGF II inhibitory effect of RA was enhanced in the presence of analogs [Leu27]IGF II (P = 0.052) but not with des(1-6)IGF II (P > 0.05), compared with wild-type IGF II.

CONCLUSIONS

These data implicate a novel antiproliferative role for RA in enhancing the pericellular clearance of IGF II via the IGF2R preventing ligand activation of the IGF I receptor. This may have broader implications for RA effects in other tumors.

Promoter and 3'-untranslated-region haplotypes in the vitamin d receptor gene predispose to osteoporotic fracture: the rotterdam study

Polymorphisms of the vitamin D receptor gene (VDR) have been shown to be associated with several complex diseases, including osteoporosis, but the mechanisms are unknown and study results have been inconsistent. We therefore determined sequence variation across the major relevant parts of VDR, including construction of linkage disequilibrium blocks and identification of haplotype alleles. We analyzed 15 haplotype-tagging SNPs in relation to 937 clinical fractures recorded in 6,148 elderly whites over a follow-up period of 7.4 years. Haplotype alleles of the 5' 1a/1e, 1b promoter region and of the 3' untranslated region (UTR) were strongly associated with increased fracture risk. For the 16% of subjects who had risk genotypes at both regions, their risk increased 48% for clinical fractures (P = .0002), independent of age, sex, height, weight, and bone mineral density. The population-attributable risk varied between 1% and 12% for each block and was 4% for the combined VDR risk genotypes. Functional analysis of the variants demonstrated 53% lower expression of a reporter construct with the 1e/1a promoter risk haplotype (P = 5 x 10(-7)) in two cell lines and 15% lower mRNA level of VDR expression constructs carrying 3'-UTR risk haplotype 1 in five cell lines (P = 2 x 10(-6)). In a further analysis, we showed 30% increased mRNA decay in an osteoblast cell line for the construct carrying the 3'-UTR risk haplotype (P = .02). This comprehensive candidate-gene analysis demonstrates that the risk allele of multiple VDR polymorphisms results in lower VDR mRNA levels. This could impact the vitamin D signaling efficiency and might contribute to the increased fracture risk we observed for these risk haplotype alleles.